Vascular access system

ABSTRACT

A connector system includes an engagement mechanism is provided that includes an engagement feature and a braided reinforcement coupled with a proximal portion of a catheter. The engagement feature can include one, two, or two or more barbs.

CROSS-REFERENCE TO RELATED APPLICATIONS

This application is a continuation of U.S. application Ser. No.12/397,275, filed Mar. 3, 2009, titled “VASCULAR ACCESS SYSTEM,” whichclaims the benefit of U.S. Provisional Application No. 61/034,125, filedMar. 5, 2008. Each of the above identified application is herebyincorporated by reference herein its entirety. Each of the followingapplications also is incorporated by reference herein in its entirety:U.S. application Ser. No. 11/600,589, filed Nov. 16, 2006, U.S.application Ser. No. 11/216,536 filed on Aug. 31, 2005, and U.S.application Ser. No. 10/962,200, filed on Oct. 8, 2004.

BACKGROUND OF THE INVENTIONS

1. Field of the Inventions

This application relates to a system for connecting multiple portions ofa fluid carrying conduit.

2. Description of the Related Art

In the United States, approximately 400,000 people have end-stage renaldisease requiring chronic hemodialysis. Permanent vascular access sitesfor performing hemodialysis may be formed by creating an arteriovenous(AV) anastomosis whereby a vein is attached to an artery to form ahigh-flow shunt or fistula. A vein may be directly attached to anartery, but it may take 6 to 8 weeks before the venous section of thefistula has sufficiently matured to provide adequate blood flow for usewith hemodialysis. Moreover, a direct anastomosis may not be feasible inall patients due to anatomical considerations. Other patients mayrequire the use of artificial graft material to provide an access sitebetween the arterial and venous vascular systems.

Although many materials that have been used to create prosthetic graftsfor arterial replacement have also been tried for dialysis access,expanded polytetrafluoroethylene (ePTFE) is the preferred material. Thereasons for this include its ease of needle puncture and particularlylow complication rates (pseudo-aneurysm, infection, and thrombosis).However, AV grafts still require time for the graft material to matureprior to use, so that a temporary access device, such as a Quintoncatheter, must be inserted into a patient for hemodialysis access untilthe AV graft has matured. The use of temporary catheter access exposesthe patient to additional risk of bleeding and infection, as well asdiscomfort. Also, patency rates of ePTFE access grafts are still notsatisfactory, as the overall graft failure rate remains high. Sixtypercent of these grafts fail yearly, usually due to stenosis at thevenous end. (See Besarab, A & Samararpungavan D., “Measuring theAdequacy of Hemodialysis Access”. Curr Opin Nephrol Hypertens 5(6)527-531, 1996, Raju, S. “PTFE Grafts for Hemodialysis Access”. Ann Surg206(5), 666-673, November 1987, Koo Seen Lin, LC & Burnapp, L.“Contemporary Vascular Access Surgery for Chronic Hemodialysis”. J RColl Surg 41, 164-169, 1996, and Kumpe, DA & Cohen, MAH“Angioplasty/Thrombolytic Treatment of Failing and Failed HemodialysisAccess Sites: Comparison with Surgical Treatment”. Prog Cardiovasc Dis34(4), 263-278, 1992, all herein incorporated by reference in theirentirety). These failure rates are further increased in higher-riskpatients, such as diabetics. These access failures result in disruptionin the routine dialysis schedule and create hospital costs of over $2billion per year. See Sharafuddin, MJA, Kadir, S., et al. “PercutaneousBalloon-assisted aspiration thrombectomy of clotted Hemodialysis accessGrafts”. J Vasc Intery Radiol 7(2) 177-183, 1996, herein incorporated byreference in its entirety.

SUMMARY OF THE INVENTIONS

In one embodiment, a system is provided for connecting components of animplantable extravascular blood conduit. The blood conduit has aproximal end adapted to couple with a first vascular segment and adistal end adapted to be inserted into a second vascular segment. Thesystem comprises a catheter, which can be configured as an outflowcomponent, and a connector. The catheter has a proximal portion and adistal portion. The distal portion is configured such that when in usethe distal portion can freely float within the second vascular segment.The proximal portion comprises an elongate body defining an inner wallhaving an inner perimeter. The inner wall also defines a blood flowlumen. The proximal portion also includes a braided structure that canbe embedded in the catheter body and disposed about the lumen. Theconnector is used to fluidly couple with the proximal portion of thecatheter. The connector has a connector body that has an outer surfacedefining a first outer perimeter and an inner surface defining a lumen.An engagement feature is disposed on an outer surface of the connectorbody adjacent a distal end thereof. The engagement feature defines asecond outer perimeter greater than the first outer perimeter. Theproximal portion of the catheter has a first configuration in the freestate wherein the inner perimeter is less than the first outer perimeterof the connector body. The proximal portion of the catheter has a secondconfiguration when in axial compression wherein the braided structureexpands to permit the inner perimeter of the catheter body to expandsuch that the proximal portion of the catheter can be advanced over theengagement feature of the connector body.

In another embodiment, a connector system is provided. The connectorsystem includes an engagement mechanism that includes an engagementfeature and a braided reinforcement coupled with a proximal portion of acatheter. The engagement feature can include one, two, or two or morebarbs.

In another embodiment, a catheter is provided for insertion into a bloodvessel at a vessel insertion site for delivering blood after dialysis toa location downstream of the vessel insertion site. The catheterincludes an elongate body and a braided structure. The elongate body hasa proximal portion, a distal portion, and a lumen extending therebetweenalong a longitudinal axis. The elongate body has an inner surfacesurrounding the lumen and an outer surface surrounding the innersurface. The distal portion of the elongate body defines across-sectional area sufficiently small to permit insertion thereof intothe blood vessel such that blood flows in the vessel around the distalportion. The braided structure has a proximal end and a distal end. Thebraided structure can be embedded within the elongate body. In oneembodiment, the outer surface of the elongate body completely surroundsthe braided structure. The braided structure extends from the proximalportion of the elongate body toward the distal portion thereof. Thedistal portion of the elongate body and the braided structure aresufficiently flexible such that the catheter can freely float at avascular location downstream of the vessel insertion site. The proximalportion of the elongate body and the braided structure are configured torespond to an axial force by expanding such that the lumen is enlargedalong the longitudinal axis for advancement over an engagement featurefor coupling the catheter with another blood conduit.

A kit is provided for accessing blood from a patient's vasculature. Thekit includes a catheter, a graft portion, and a connector forinterconnecting the catheter and the graft portion. The connectorincludes an engagement feature configured to radially deform a proximalportion of the catheter. The proximal portion of the catheter includes areinforcement member that increases the force needed to disconnect thecatheter from the connector, such that the force to disconnect isgreater than a force to connect the catheter and the connector.

In another embodiment, a method of assembling a blood flow conduitin-situ is provided. The method includes providing a proximal bloodconduit portion and a distal blood conduit portion. The distal bloodconduit portion includes a catheter in some embodiments. The distalblood conduit can comprise a proximal end portion in which a braidedstructure is embedded. The method includes cutting the distal bloodconduit through the braided structure to size the distal blood conduitin-situ and distal blood conduit the catheter to the proximal bloodconduit portion.

BRIEF DESCRIPTION OF THE DRAWINGS

The structure and method of using the invention will be betterunderstood with the following detailed description of embodiments of theinvention, along with the accompanying illustrations, in which:

FIG. 1 is a perspective view of a vascular access system having aproximal end adapted to couple with a first vascular segment and adistal end adapted for insertion into a second vascular segment;

FIG. 2 is a perspective view of a catheter that has a distal portionadapted for positioning in a blood vessel and a proximal portionconfigured to provide an enhanced connection to another blood conduit;

FIG. 2A is a schematic view of a distal portion of the catheterillustrating techniques for embedding a braided structure therein;

FIG. 3 is a side view of a reinforcement member configured to beincorporated into the blood flow conduit of FIG. 2;

FIG. 3A is an end view of one braided member of the braided structure ofFIG. 3;

FIG. 4 is a plan view of a connector that is adapted to couple a firstblood flow conduit with a second blood flow conduit;

FIG. 5 is a graph illustrating a retention force for various engagementmechanisms described herein;

FIG. 6 is a graph illustrating a retention force corresponding tovarious techniques for connecting an engagement mechanism having twobarbs;

FIG. 7 is a graph illustrating a retention force for an engagementmechanism having a braided structure with different pic counts; and

FIG. 8 is a graph of attachment forces for various embodiments.

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENT

This application relates to new vascular access systems, new connectorsystems, and new fluid-carrying conduits. The fluid carrying conduitsare arteriovenous (AV) shunts or catheters in various embodiments. Someof the embodiments described herein may be incorporated into ahemodialysis system.

Hemodialysis treatments and vascular access devices therefore arediscussed in greater detail in U.S. patent application Ser. Nos.10/962,200 (US Publication No. 2005-0137614-A1), 11/216,536 (USPublication No. 2006-0064159 A1), and 11/600,589 (US Publication No.2007-0167901 A1) and in U.S. Pat. Nos. 6,102,884 and 6,582,409. Theembodiments described herein can be combined with the systems andmethods of any of these applications and patents, all of which arehereby incorporated by reference in their entirety.

As will be understood in view of the description herein provided, thenew connector systems and apparatuses can improve one or more areas ofperformance of vascular access systems. For example, the embodimentsdescribed herein improve in-situ connection of a catheter, or otherblood-carrying conduit, configured for use as an outflow component, toanother component or device of a vascular access system.

In some embodiments, a reinforcement member can be incorporated into thevascular access system (e.g., in a proximal portion of a catheter orother blood carrying conduit) to enhance the security of a connectionbetween a catheter and another component of the vascular access system.In some cases, the reinforcement member also extends through asubstantial portion of the length of a blood carrying conduit toimproves kink and crush resistance of the fluid carrying conduit. Theseand other advantages of the new devices and methods described hereincould be useful in a number of environments that employ a vascularaccess system, such as vascular access devices, ventricular assistdevices, total artificial hearts, and various types of hemodialysissystems.

Environments in which these improvements could be used includeshort-term applications (e.g., several days to a week) and longer-termapplication. For example, the improvements described herein are usefulin longer-term applications of 30 days or more. The improvementsdescribed herein are useful in longer-term applications of 90 days ormore. In some cases, the improvements described herein are useful inlong-term applications of 1 year or more. The embodiments describedherein can be incorporated into short-term and into longer-termapplications for dialysis.

As will be discussed below, a braided structure can be incorporated intoa fluid-carrying conduit. In some embodiments, the braided structure canbe embedded in an elongate body of the fluid-carrying conduit, providinga smooth relatively constant outer surface. The braided structure canimprove the security or integrity of the connection between theblood-carrying conduit and other structures to which it is attached. Invarious embodiments, these innovations provide greater durability andmanufacturability. In addition, the implantation process can beenhanced, such as by providing better connectability and, in some cases,a tactile confirmation of the security of a connection, as discussedbelow. In some cases, a visual confirmation of the security of aconnection can be provided.

FIG. 1 depicts one embodiment of a vascular access system 10 that isconfigured to shunt blood from a first vascular segment to a secondvascular segment. The vascular access system 10 can take any suitableform, but preferably the system is adapted to be implanted beneath theskin of the patient. In one embodiment, the vascular access system 10 isimplanted primarily extravascularly, though a distal portion thereof mayreside in or extend through a blood vessel. The vascular access system10 can be partly or completely implanted. Various techniques forimplanting are discussed below, including placement of at least aportion of the system 10 in a vascular segment. Also, the vascularaccess system 10 can be implanted in a subcutaneous tunnel, as discussedfurther below. Additional details of processes for implantation arediscussed in the patents and applications listed above, which areincorporated by reference herein.

The vascular access system 10 has a proximal end 14 and a distal end 18and a lumen 20 that extends between the proximal and distal ends 14, 18.The proximal end 14 can be adapted to couple with, e.g., attached to, afirst vascular segment and the distal end 18 can be adapted to becoupled with, e.g., inserted into a second vascular segment. The lumen20 preferably extends between the proximal and distal ends 14, 18 andprovides a pathway for blood to flow between the first and secondvascular segments. The lumen 20 also can be accessed from outside thepatient to facilitate dialysis or other treatment.

The first and second vascular segments are arterial or venous vascularsegments in various techniques. For example, the proximal end 14 can beadapted to be coupled with a brachial artery or other artery thatresides close to the skin. Any suitable coupling between the proximalend 14 and the first vascular segment can be used. In one embodiment theproximal end 14 can be attached by an end-to-side anastomosis to abrachial artery. The distal end 18 can be adapted to couple with orextend into a vein, e.g., in the central venous system, as discussedbelow and in the application incorporated by reference herein.

In one embodiment, the vascular access system 10 includes a plurality ofcomponents that can be assembled to form the lumen 20. In oneembodiment, a first blood carrying conduit 22 extends from the proximalend 14 toward the distal end 18 and a second blood carrying conduit 26extends from the distal 18 toward the proximal end 14. In one embodimenta third blood carrying conduit 30 is positioned between the first andsecond blood carrying conduits 22, 26. As discussed below, the thirdblood carrying conduit 30 is adapted to connect the first and secondblood carrying conduits 22, 26 together in various embodiments.

Where provided, the third blood carrying conduit 30 enables the firstand second blood carrying conduits 22, 26 to have differentcharacteristics that are well suited for the unique ways in which theseconduits interact with the vasculature. For example, the first bloodcarrying conduit 22 can be specifically configured to be integrated intothe vessel with which it is coupled, e.g., by anastomosis connection toan artery. Also, the second blood carrying conduit 26 can bespecifically configured to interact with a vascular segment to minimizethe likelihood of adverse side effects, e.g., by being flexible orotherwise formed to enable a distal portion of the conduit 26 to extendinto the central venous system and interact in an atraumatic manner withvessel walls and other tissues in the vasculature or heart. Thus, thisinnovation pertains to the unique requirements of a device that performboth as a permanently implanted extravascular graft and as anintravascular catheter.

The vascular access system 10 can be configured with an engagementmechanism 32 that enhances the security of a connection between twoblood carrying conduits of the system. The engagement mechanism 32 caninclude multiple portions with at least one portion located on thesecond blood carrying conduit 26 and at least one portion is located onthe third blood carrying conduit 30. In some embodiments, the engagementmechanism 32 is configured such that the connection formed therebyrequires a greater force to disconnect than is required to connect thesecond and third blood carrying conduits 26, 30. This provides greatersecurity of and confidence in the connection at the engagement mechanism32.

In various embodiments, the engagement mechanism 32 includes anengagement feature 33 located on one of the second and third bloodcarrying conduits 26, 30 and an enlargeable portion 34 on the other ofthe second and third blood carrying conduits 26, 30. For example, asdiscussed in more detail below, the third blood carrying conduit 30 caninclude at least one barb and the second blood carrying conduit 26 canbe formed to apply an inward and sometimes distally directed force onthe barb to resist disconnection of the conduits. In one embodiment, adistal portion of the third blood carrying conduit 30 includes twobarbs. In one embodiment, the second blood carrying conduit 26 includesa braided structure or other expandable reinforcement member 35 thatgenerates a compressive force on the barb or barbs to enhance thesecurity of the engagement mechanism 32. FIG. 1 only shows the braidedstructure partially for clarity. As discussed further below, the braidedstructure can extend to the proximal end 14 and toward the distal end18. Various additional examples of features of engagement mechanisms arediscussed below.

In some embodiments, the vascular access system 10 also includes anengagement mechanism 36 that facilitates coupling the first bloodcarrying conduit 22 with a distal portion of the lumen 20. As discussedfurther below, the engagement mechanism 36 can be incorporated into aproximal portion of a connector. In other embodiments, the first andthird conduits 22, 30 can be unitary in construction such that theengagement mechanism 36 is not required.

The first blood carrying conduit 22 can take any suitable form forproviding fluid communication between a patient's vascular system andthe lumen 20. In one form the first blood carrying conduit 22 is a graftformed of a suitable material, e.g., ePTFE. In some applications, it isdesirable to provide access to the lumen 20 very soon after implantationof the system 10. Various features for enabling access very soon afterimplantation, if not immediately thereafter, are discussed in theapplications incorporated by reference herein above, including U.S.application Ser. Nos. 11/216,536 (US Publication No. 2006-0064159 A1)and 11/600,589 (US Publication No. 2007-0167901 A1). Other suitablebiocompatible materials can be used and these will be apparent to oneskilled in the art.

Although illustrated in an AV shunt context, the engagement mechanism isalso relevant to other context. Accordingly, the first blood carryingconduit 22 could be a proximal portion of a connector, or a component ofanother system that conveys blood, e.g., in a ventricular assist device.

In one embodiment, the second blood carrying conduit 26 is configured asa catheter for returning blood to a patient's vasculature. In someembodiments, the conduit 26 is an outflow component of the system 10.The catheter preferably is adapted such that, in use, at least a distalend portion thereof can freely float within a vascular segment when thevascular access system 10 is applied to a patient. This feature reflectsresearch that indicates that graft failures from localized stenosis atthe venous end of AV grafts are primarily due to intimal hyperplasia,compliance mismatch between the graft and the native vein anastomosis,and turbulent flow at the anastomosis site. Kanterman R. Y. et al“Dialysis access grafts: Anatomic location of venous stenosis andresults of angioplasty.” Radiology 195: 135-139, 1995. We hypothesizethat these causes could be circumvented by eliminating the venousanastomosis and instead, using a fluid carrying conduit to discharge theblood directly into the venous system. We have developed vascular accesssystem that eliminates the venous anastomosis in the AV shunt, using acatheter element at the venous end and a synthetic graft elementanastomosed to the artery in the standard fashion. We believe that suchsystem should eliminate or reduce venous hyperplasia, which is thelargest reason for AV shunt failure.

Accordingly, configuring the second blood carrying conduit 26 (e.g., adistal portion thereof) to freely float provides atraumatic interactionwith the blood vessel. Such a configuration also can minimize thelikelihood of damage to the vessel in which the distal end portionresides by minimizing trauma to the vessel.

In some embodiments, the conduit 30 or portions thereof can beintegrated into another component, e.g., into the first blood carryingconduit 22. Thus, the system 10 can be configured with less than three,e.g., only two, separate blood carrying conduits. Additionally, theprimary function of the third blood carrying conduit 30 is to couple thefirst and second blood carrying conduits 22, 26 and thus the third bloodcarrying conduit need not be exposed to blood or form a part of thelumen 20 in all embodiments.

FIG. 2 shows one embodiment of a catheter 100 that can be used in thevascular access system 10. As used herein “catheter” is a broad termthat includes any blood carrying conduit that can be at least partiallyinserted into a blood vessel and advanced therein to a selectedlocation, including into the atrium. The catheter 100 can take anysuitable form, consistent with the below description. In someembodiments, the catheter is configured as an outflow component.

The catheter 100 has a proximal portion 104, a distal portion 108, andan elongate body 112 that extends therebetween. In some applications,the catheter 100 is configured such that the proximal portion 104 isconnectable over a barb, as discussed below, to enhance securement ofthe catheter 100 to a connector, which can be incorporated into theconduit 30. The proximal portion 104 preferably also is trimmable suchthat the length of the catheter 100 can be determined in-situ. In oneembodiment, the catheter 100 also has a sizing region 114 thatfacilitates customizing the size of the catheter 100 to the patient. Inone embodiment, the sizing region 114 is located in the proximal portion104 of the catheter 100. As will be discussed further below, the sizingregion 114 can be trimmed or cut through to reduce the length of thecatheter 100. Preferably the sizing region 114 is configured to be cutby hand using any standard cutting implement that would be present inthe operating room, such as surgical scissors.

The elongate body 112 preferably defines an inner wall 116 thatsurrounds a blood flow lumen 120. The inner wall 116 has an innerperimeter 124 that in part defines the blood flow capacity of thecatheter 100. In one embodiment, the blood flow lumen 120 issubstantially cylindrical and the inner wall 116 and the inner perimeter124 define are substantially circular in cross-section. In oneembodiment, the blood flow lumen 120 has an inner diameter of about 5.0mm. Lumens of other shapes can be used as well, as will be understood byone skilled in the art. Forming the lumen 120 to have a 5.0 mm diameterlumen provides a benefit of being able to handle sufficient blood flowfor dialysis while permitting the outer size of the catheter 100 to besmall enough to be insertable into the internal jugular vein in onetechnique. The outer size and inner perimeter 124 of the catheter 100can be substantially constant through the length of the lumen 120 or canvary as will be understood by one skilled in the art.

The elongate body 112, particularly the inner wall 116 can be configuredto provide adequate hemocompatibility such that blood flowingtherethrough is not damaged or adversely affected thereby. The bloodflow lumen 120 preferably is configured to convey blood in asubstantially atraumatic manner between the portions 104, 108. In oneembodiment the inner wall 116 is sufficiently smooth in surface finishto minimize turbulence at the wall. If the catheter 100 is integratedinto the vascular access system 10 (e.g., as the second blood carryingconduit 26), the lumen 120 can form a portion of the lumen 20. Otherportions of the lumen 20 can be defined in one or both of the first andthird blood carrying conduits 22, 30.

The catheter 100 preferably is configured such that in use the distalportion 108 can freely float within a vascular segment. As discussedelsewhere herein, the system 10 can be applied such that the distalportion 108 is positioned in, extends within, or is inserted through ablood vessel, e.g., in the central venous system. Accordingly, thedistal portion 108 preferably is configured to have a smaller outer sizethan the vessel in which it resides. This enables blood to pass aroundthe distal end portion 108. For example, the distal portion 108 canreside in the central venous system in such a manner that blood flowsbetween an outer surface of the distal portion 108 and an inner surfaceof the blood vessel. In one embodiment, the distal portion 108 of thecatheter 100 has an outer perimeter that is substantially circular withan outer diameter of about 6.1 mm. In comparison, the typical vesselthrough which the distal portion 108 can be inserted is about 8-20 mm.Although larger catheters can be used for some patients and for someother applications, 6.1 mm is a size that is particularly well suitedfor insertion into an internal jugular vein of an adult human patient.Smaller catheters can be used for certain techniques, e.g., for moreperipheral applications.

The dimensions of the system 10 and the components described herein thatcan be used in the system 10 are not limiting. Rather the dimensionsprovide examples of specific embodiments. For other applications, otherdimensions may be appropriate. For example, the outer diameter of thedistal portion 108 of the catheter 100 need not be 6.1 mm but ratherwould be a function of the vessels into which it is to be inserted. Inother applications currently contemplated, the outer diameter of thedistal portion 108 could be about four mm to about 8 mm.

Additionally, as discussed below, the distal portion 108 preferably isformed to be relatively flexible. The flexibility permits the distalportion 108 to relatively gently interact with the blood vessel in whichit resides. In one application, the catheter 100 is applied through asuperficial vessel and is advanced through the internal jugular veintoward the heart. In this environment, a relatively low stiffnessconstruction is sufficient for delivery of the distal portion 108 thecatheter 100.

FIG. 2A illustrates one approach to making the catheter 100 moreflexible in which a soft material is incorporated into the elongate body112. In various embodiments, all or a portion of the elongate body 112can be formed of any suitable flexible elastomer, such as polyurethane,CFlex, SIBS (styrene isoprene butadiene) or polyolephins. In oneexample, silicone tubing can be used in an inner portion 100A of thecatheter 100. More generally, the elongate body 112 can be formed of animplantable thermoplastic elastomer. In one embodiment, silicone tubinghas a durometer of about 50 Shore A or less is used to form the innerportion 100A of the catheter 100. In some applications, the catheter 100can be formed of a material having a durometer of 30-80 Shore A willperform adequately. In other embodiments, a higher or lower durometermaterial can be used. As further discussed below, there can beparticular advantages to the softer durometers of 30-60 Shore A and40-50 Shore A. As discussed further below, an outer portion 100B of thecatheter 100 can be formed of a similar or the same material as theinner portion 100A.

In various embodiments, the base material preferably is flexible andbase material strength is less critical. In this application, theability for the braided tubing to expand radially over a connector barbsis preferred. As mentioned previously this is an advantage of a braidedreinforcement over a single filament, coiled reinforcement, which cannotexpand to slip over a barb. This is similarly an advantage of braidreinforced tube using a softer base material (such as one with arelatively low durometer, e.g., <70 Shore A) over one with a harder basematerial. Forcing a braided tube with a hard base material over a barbwould require an unacceptably high force. Furthermore, under the forcesanticipated to be applied during in use, a braided tube with a harderbase material would not provide the degree of necking that is desirablein some clinical situations.

The catheter 100 also can include a braided structure 140 or otherreinforcing member between the inner portion 100A and the outer portion100B. The braided structure 140 provides a number of benefits to thecatheter 100. For example, the braided structure 140 can be configuredto contribute to at least in part, resistance to radial compression ofthe elongate body 112. Also, the braided structure 140 can be configuredto provide at least in part, resistance to kinking of the elongate body112.

In one embodiment, the braided structure 140 is provided primarily toenhance the security of a connection between the catheter 100 andanother component of a blood carrying system, such as the vascularaccess system 10. For example, the braided structure 140 can enhance thesecurity of an engagement mechanism of which the braided structure formsa part.

In one embodiment, the braided structure 140 includes a proximal end 144and a distal end 148. The braided structure 140 can be disposed aboutthe lumen 120, e.g., substantially or completely surrounding the lumen.The braided structure 140 also can extend along the lumen 120 such thatthe proximal end 144 is within the proximal portion 104 of the elongatebody 112 and the distal end 148 is within the distal portion 108 of theelongate body. In one embodiment, the braided structure 140 isconfigured such that the proximal end 144 extends to or adjacent to theproximal end of the elongate body 112.

In one embodiment, the braided structure 140 is configured such that thedistal end 148 is located proximal of the distal end of the elongatebody 112. For example, the distal end 148 of the braided structure 140can be located about 0.2 inches, about 0.25 inches, or from about 0.2 toabout 0.25 inches proximal of the distal end of the catheter 100. Thisarrangement permits a device for visualization to be located distal ofthe distal end 148 of the braided structure 140. For example, aradiopaque marker 149 can be located in the distal portion 108 of theelongate body. In one embodiment, the radiopaque marker 149 is a ringformed of platinum iridium or another radiopaque material. Any othersuitable device to provide the clinician with an indication of where thedistal portion 108 of the catheter 100 is located when the blood flowconduit is being advanced in the vasculature can be used instead of theradiopaque marker 149 as will be understood by those skilled in the art.

Also, the configuration of the braided structure 140 can be varied alongthe length of the catheter to optimize certain performance metrics ofthe catheter. For example, as discussed herein, the distal portion 108preferably is relatively flexible to minimize trauma to the patient'svasculature. This can be achieved by varying the pic count of thebraided structure 140. Additionally, a proximal portion of the braidedstructure 140 can be optimized to enhance the connection strength of anengagement mechanism as discussed herein.

FIG. 2A illustrates that the braided structure 140 can be embedded inthe elongate body 112. In one embodiment, the braided structure 140 isembedded in the elongate body 112 such that an outer surface of theelongate body 112 surrounds the braided structure 140. In some cases,the braided structure 140 is disposed within the elongate body 112 suchthat the outer surface of the elongate body 112 is substantially smoothalong the longitudinal axis of the catheter body. When embedded in theelongate body 112, the braided structure 140 also can be disposedradially outside of the inner wall 116 of the elongate body 112. Thebraided structure 140 also can be disposed radially between the innerwall 116 of the elongate body 112 and an outer surface thereof.

Although the catheter 100 is relatively soft, the braided structure 140provides reinforcement that prevents or substantially minimizes kinking,crushing, and other phenomenon that can cause at least partial collapseof the lumen 120. Collapse of the lumen 120 can occur when the catheter100 traverses a bend of relatively small radius. For example, in someapplications the catheter 100 is required to traverse a joint, such asthe shoulder of a patient. Such a traverse could require a relativelysmall bend radius. In other applications, the catheter 100 need nottraverse a small bend radius (e.g., when not crossing a joint). In someapplications, a preferred routing of the catheter 100 may cause theconduit to traverse a bend with a radius of about 1.0 inch. In someapplications, a preferred routing of the catheter 100 may cause theconduit to traverse a bend with a radius of 1.0 inch or more. In otherapplications, in a preferred routing the catheter 100 may have totraverse a bend with a radius of about 0.25 inch. In other applications,in a preferred routing the catheter 100 may have to traverse a bend witha radius of about 0.5 inch. In other applications, in a preferredrouting the catheter 100 may have to traverse a bend with a radius ofbetween about 0.25 inch and about 1.0 inch. In all of these cases, thebraided structure 140 provides a reinforcement to prevent orsubstantially minimize collapse of the lumen 120.

Properties of the braided structure 140 and variations thereof result indesirable kink minimizing properties not achievable using a coilreinforcement. At very small bend diameters, the braided structure 140is expected to gradually flatten, instead of suddenly inflecting to akinked configuration. This is advantageous for several reasons. First,gradual flattening of the braided structure 140 will be detectable by aclinician (e.g., using an imaging technology such as X-Ray imaging) suchthat the clinician can recognize that a less than desirable bend radiusis present before full narrowing of the blood conduit occurs. Secondly,a coil reinforcement undergoes higher strain levels and alternatingstrains than the braided structure 140. This prevents or delaysundesirable fracture or failure due to repeated flexure at very smallbend radii. In addition, only a fraction of the plurality of members inthe braided structure 140 undergo significant stress or strain level atminimum bend radii. The braid members on the top and bottom of the foldundergo negligible stress compared to the members at the sides of thefold. This means that even if the loading conditions were severe enoughto fracture braid members on the sides of the fold, the majority ofbraid members at the fold would not fracture and the device would remainsubstantially intact. In previous single filament, coil reinforceddevices, any fracture was potentially catastrophic. Also, the disclosedbraid configurations advantageously exhibit full narrowing or kinking ata much smaller bend radii than prior coil reinforced devices. Prior coilreinforced devices had a kink radius of approximately 0.5 inch, whereasvarious embodiments of the catheter 100 have a kink radius ofapproximately 0.2 inches.

In some embodiments, the braided structure 140 forms a part of anengagement mechanism, similar to the engagement mechanism 32.

FIG. 3 illustrate further details of one embodiment of the braidedstructure 140. In one embodiment, the braided structure 140 has aplurality of braid members 152 that overlap each other in the structure.The braided structure 140 can comprise a shape memory material, such asa nickel titanium alloy (e.g., a NITINOL® alloy) in various embodiments.Other suitable materials include stainless steel (e.g., 304 or 316),titanium, glass, Kevlar and other similar fibrous materials. Forexample, each of the braided members 152 can comprise a nickel titaniumalloy or other shape memory material. In some embodiments, the braidedmembers 152 are woven together to form the braided structure 140. Thebraid members 152 can have a cross-section with a first transversedimension D1 being greater than a second transverse dimension D2, thefirst transverse dimension D1 being perpendicular to the secondtransverse dimension D2. In one embodiment, the second transversedimension D2 (e.g., the shorter of the two dimensions) is generallyradially extending relative to the longitudinal axis of the lumen 120.These embodiments are illustrated by FIG. 3A.

Such an arrangement can minimize the thickness of the elongate body 112between the inner wall 116 and the outer surface of the elongate body.This can result in a very thin structure, e.g., with a thickness ofabout 2.0 mm or less. In one embodiment, the thickness of the catheter100 between the inside wall 116 and an outer surface of the catheter isabout 1.1 mm. In one embodiment, the thickness of the braided member 152is less than about 50 percent of the thickness of the elongate body 112.In one embodiment, the thickness of the braided member 152 is less thanabout 25 percent of the thickness of the elongate body 112. In oneembodiment, the thickness of the braided member 152 is about 10 percentof the thickness of the elongate body 112. Minimizing the thickness ofthe wall of the catheter is important in some embodiments because it canmaximize the size of the lumen for carrying blood while stillmaintaining the ability to insert the catheter 100 into selectedvessels.

By reducing the dimension D2, the crossing profile of the catheter 100can be reduced or minimized. Reducing the crossing profile provides anadvantage of permitting access to the vascular system through a smallerincision. In some embodiments, by reducing the dimension D2, the size ofthe lumen 120 can be increased for a given crossing profile. Increase inthe size of the lumen 120 is advantageous in that it permits greaterfluid carrying capacity in the lumen. The braided structure 140 providesconsiderable kink and crush resistance and relative flexibility of theelongate body 112.

One embodiment illustrated by FIG. 3A provides a plurality of braidedmembers 152 that have elongate cross-sections provided by a plurality ofaxi-symmetric side-by-side wires. For example, a braided member couldinclude two circular cross-section wires provided in a side-by-sidearrangement. In this embodiment, the radial dimension (D2) of thebraided members 152 is about equal to the diameter of the wires and thedimension transverse to the radial dimension (D1) is about equal totwice the diameter of the wires. One useful construct for the braidedmembers 152 incorporates two 0.005 inch wires that are formed of anickel titanium alloy. Other embodiments could incorporate 0.006 inch orlarger wires. Some embodiments could incorporate 0.004 inch or smallerwires. Larger wires may be suitable for larger catheters or forcatheters that can use smaller lumens. Smaller wires may be suitable forsmaller catheters or for catheters subject to less crush or kink forces.In other embodiments, the braided members 152 can be formed with one ormore flat or oval cross-section wires. A suitable alloy would include 56weight % nickel and 44 weight % titanium. This material can be treatedto provide suitable properties, such as by a straight annealing. A lightoxide finish is suitable for some embodiments.

Any suitable woven pattern can be provided for creating the braidedstructure 140. For example, a hopsack weave can be employed in which thebraided members 152 cross over a first transverse braided member thencross under a second transverse braided member adjacent the firsttransverse braided member. This pattern can be repeated throughout thebraided structure 140 to provide a suitable weave. Hopsack weave issometimes referred to as a diamond pattern full load. In otherembodiments, the weave could be a diamond pattern half-load or aherringbone weave, which will be understood by one skilled in the art.Other weave arrangements that can be used include a linen weave, forexample. However, for some applications, the linen weave is not expectedto perform as well as other weave patterns discussed herein.

Further aspects of the braided structure 140 can affect its performance.For example, the density and configuration of the braided members 152can affect the degree of security when the catheter 100 is engaged withanother blood carrying component. For example, in one embodiment, thebraided structure 140 is formed with a suitable helix angle, which isdefined as the angel between any of the braided members 152 and alongitudinal axis of the braided structure 140. A helix angle within arange of about 40 degrees to about 65 degrees could be used in someembodiments of the braided structure 140. In other embodiments, thebraided structure 140 can be formed with a helix angle in the range ofabout 50 degrees to about 55 degrees. In one embodiment the braidedstructure 140 defines a helix angle of about 51 degrees. In oneembodiment the braided structure 140 defines a helix angel of about 54degrees. A higher helix angle creates a more flexible catheter. A lowerhelix angle provides less flexibility but is easier to advance over aconnector as discussed below. Lower helix angle also provides a lesscrush resistant catheter, which is less optimal in some applications.

Another aspect of the braided structure 140 that relates to theperformance of the engagement mechanism 32 of which the braidedstructure may be a part is the pic count (crossings per unit length) ofthe braided structure 140. One skilled in the art will recognize thatpic count and helix angle are related. More particularly, pic count canaffect the connectability of the catheter 100 with a connector, whichcan form a part of the third blood carrying conduit 30. Greater piccount corresponds to a higher force required for coupling the engagementmechanism 32. Lesser pic count corresponds to lower connecting forces.Catheters with lower pic counts are more subject to kinking. In oneembodiment, the braided structure 140 has a pic count between about 21ppi and about 24 ppi. In another embodiment, the braided structure 140has a pic count of between about 22-24 ppi when assembled on thecatheter 100. In another embodiment, the braided structure 140 has a piccount of about 21 ppi. In another embodiment, the braided structure 140has a pic count of about 23 ppi. In another embodiment, a pic count of22 ppi would be suitable.

FIGS. 7 and 8 illustrate a comparison of the retention force andattachment force respectively for various embodiments of an engagementmechanism. In this study, pic count of a braided structure in a catheterand various aspects of the engagement feature 240 of the connector 200were varied. The variables that were varied in the connector 200 areshown in the table below, with all dimensions being in inches):

Spacing Between Height Length of Length of Barbs 244 Height of of barbBarb 244 Barb 248 and 248 barb 244 248 Embodiment 1 0.065 0.065 0.2400.012 0.012 Embodiment 2 0.065 0.05 0.225 0.012 0.011 Embodiment 3 0.0650.05 0.240 0.012 0.011 Embodiment 4 0.065 0.04 0.240 0.012 0.009

FIG. 8 shows a general trend to lower attachment forces for Embodiment 4compared to other embodiments. Embodiment 4 had lower values for theheight and the length of the barb 248. Also, FIG. 8 shows that a lowerpic count of the braided structure of the catheter can result in asignificantly lower attachment force compared to a higher pic countarrangement, where the connector has two barbs. Lowering the attachmentforce is desirable in some embodiments to provide faster and easierassembling of a vascular access system in-situ for the clinician.

FIG. 7 shows that for the embodiments described in the table above,retention force (e.g., the force needed to disconnect the catheter 100from the connector 200) was not highly dependent on pic count for theembodiments of the connector studied. Although there is an increase inretention force for Embodiment 2 compared to the other embodiments, allfour embodiments had relatively high retention forces compared to anengagement mechanism including a connector with a single barb engagedwith a catheter having a braided structure.

Also, the performance of the braided structure 140 can relate to thenumber of wires incorporated into the weave. In some embodiments, thebraided structure 140 includes about forty-eight braided members 152.Other numbers of braided members 152 can be provided, however. Forexample, in one embodiment, twenty-four braided members 152 can beprovided. Fewer wires provide less crush and kink resistance. More wiresprovide greater resistance in the braided structure 140 to kinking andcrushing. Other numbers of wires for forming the braided structure 140can also be used, as will be understood by one skilled in the art.

Techniques for Forming Blood Carrying Conduits

Various techniques are contemplated for forming the catheter 100 withinner and outer portions 100A, 100B. In some techniques, the outerportion 100B is formed in a different process than the inner portion100A. For example, the in a first step of one embodiment, an elongatetubular section of silicone or a flexible elastomer is slid onto a solidmandrel to provide the inner portion 100A. The tubular section can havea durometer of about 50 shore A or any other suitable hardness asdiscussed herein. The tubular section optionally is loaded with bariumsulphate. In one technique, the inner diameter of the tubular section isabout 5.0 mm and the outer diameter of the tubular section is about 5.5mm.

Thereafter, the braided structure 140 can be placed over the outersurface of the inner portion 100A. The braided structure 140 can have adiameter of about the same as that of the tubular section outerdiameter. In one embodiment, the braided structure 140 has an innerdiameter of about 5.5 mm. In one embodiment, the braided structure 140has an inner diameter of slightly less than the outer diameter of thetubular section. For example, an inner diameter of about 5.4 mm for thebraided structure 140 would be suitable. This arrangement causes thebraided structure 140 to cinch down on the outer surface of the tubularsection forming the inner portion 100A. In one technique, the braidedstructure 140 is sized such that its length is substantially the same asor slightly less than that of the tubular section.

Thereafter a platinum iridium marker band (or visualization device ofother configuration) is positioned over the inner portion 100A. This canbe achieved by sliding the marker band over the distal end to a locationbetween the distal end of the braided structure and the distal end ofthe tubular section. In another technique, strands of the braidedstructure 140, particularly strands located in the distal portionthereof, can be configured to be visible using radiography or anothersimilar technique.

Thereafter, the assembly formed to this point in the process can becovered with a suitable material to form the outer portion 100B of thecatheter 100. For example, the assembly can be coated with a suitablematerial to form the outer portion 100B of the catheter 100. In onetechnique, the outer portion 100B is formed by dip or spray coatingsilicone, polyurethane or other suitable material over the assembly. Inanother technique, the outer layer can placed over the assembly andbonded, shrunk, thermally fused or otherwise formed together. In anothertechnique, the outer layer can be formed by in-line extrusion over theassembly.

Other optional steps can thereafter be performed in various embodiments.For example, the construct can be cut to size and luer fittings (orother suitable connectors) can be formed on a proximal end thereof asneeded. The forgoing steps are illustrative and need not be performed inthe order recited.

Engagement Features & Mechanisms

As discussed above, in various embodiments, the braided structure 140extends to the proximal portion 108 of the catheter 100. At least theportion of the braided structure 140 that so extends can interface withthe blood carrying conduit 30 forming a part of the engagement mechanism32.

FIG. 4 illustrates one embodiment of a connector 200 that can beincorporated into the blood carrying conduit 30 of the system 10. Theconnector 200 includes a connector body 202 that has a proximal portion204, a distal portion 208, and lumen 212 extending therebetween. Thelumen 212 can take any suitable form. In one embodiment, the lumen 212includes a tapered section similar to that described in U.S. applicationSer. No. 10/962,200.

The proximal portion 204 preferably is configured to interface with,e.g., be coupled to, the blood carrying conduit 22. The connectionbetween the connector 200 and the conduit 22 can be achieved in anysuitable manner. For example, the proximal portion 204 can have anenlarged portion 214 over which the conduit 22 can be advanced. Theenlarged portion 214 can comprise a portion of the engagement mechanism36. Other techniques and structures for connecting the connector 200 andthe conduit 22 are described in the applications incorporated byreference herein above, including U.S. application Ser. Nos. 11/216,536and 11/600,589.

The distal portion 208 is configured to interface with the bloodcarrying conduit 26 or with the catheter 100. In one embodiment, thedistal portion 208 includes an outer surface 220 that extends between adistal end 224 and a proximal end 228 of the connector 200. In oneembodiment, the outer surface 220 extends from the distal end 224 to aproximal end of the distal portion 208, adjacent to an enlarged segment250. The connector 200 also includes an engagement feature 240 that isdisposed on the outer surface 220. In one embodiment, the engagementfeature 240 comprises a portion of an engagement mechanism.

The engagement feature 240 can take any suitable form. For example, inone embodiment, the connector body 202 has a first outer size CB1 andthe engagement feature 240 has a second outer size CB2 that is greaterthan the first outer size CB1. The outer sizes CB1, CB2 can correspondto diameters in one embodiment, but could correspond to outerperimeters. In one embodiment, CB1 is a diameter of about 5.4 mm. In oneembodiment, CB2 is a diameter of about 6.0 mm. As discussed above, theinner diameter of the catheter 100 is about 5.0 mm in one embodiment.This corresponds to a prestressing of about 1 mm in the diameter of thecatheter 100. In some embodiments, a prestressing of about 20% of theinner diameter of a catheter being inserted over the engagement feature240 can provide suitable connectability. In some embodiments, a suitableamount of prestressing (e.g. enlargement of the inner diameter of acatheter connected over the engagement feature 240) can range from16-24%. In other embodiments, a suitable amount of prestressing (e.g.enlargement of the inner diameter of a catheter connected over theengagement feature 240) can range from 8-28%.

Prestressing, or stretching the inner size of the catheter 100 createsan enhanced security of the connection formed by the engagementmechanism 32. In particular, the braided structure 140 and the proximalportion of the catheter 100 expand upon being placed in compressionduring the distal advancement of the connector 200 relative to thecatheter. After advancement, the braided structure 140 seeks to returnto its pre-formed shape, which produced an inwardly directed force onthe connector 200 increasing the security of the engagement between theconnector 200 and the catheter 100. Also, the configuration of thebraided structure 140 is such that if a force for disconnecting theconnector 200 and the catheter 100 is applied, the braided structurewill increase the inwardly directed force further securing theconnection. This action at the engagement mechanism is analogous to aChinese finger trap toy, which reduces in cross-sectional size uponelongation.

Providing one or more barbs creates an even more secure connection. Insome embodiments, the engagement feature 240 includes a barb 244 thatextends over a portion of the connector body 202. The barb 244 caninclude any structure that includes a raised surface that extends toabove the connector body.

FIG. 4 illustrates that in one embodiment a second barb 248 is providedbetween the first barb 244 and the proximal portion 204 of the connector200. As discussed below, the second barb 248 of the engagement featuregreatly enhances the security of the connection between the catheter 100and the connector 200. The second barb 248 can take any suitable form.In some embodiments of the connector 200, the second barb 248 is smallerthan the first barb 244. For example, the second barb 248 can be about5.8 mm in diameter in one embodiment. The first barb 244 can be about5.99 in diameter.

In some embodiments, the height of the engagement feature 240 (e.g., thebarbs 244 or 248) can be important. Barb height can be measured on thedistance from a location of the barb that is farthest radially from anaxis of the lumen through the connector 200 to the surface 220 adjacentto the barb 244, 248. In one embodiment, this distance is between about0.005 inches and about 0.020 inches. In one embodiment, the height ofthe engagement feature is about 0.013 inches. In one embodiment, theheight of the engagement feature is about 0.012 inches. In oneembodiment, the height of the engagement feature or barb is betweenabout 0.008 inches and about 0.009 inches. In one embodiment, the heightof a first barb of the engagement feature 240 is about 0.012 inches andthe height of a second barb of the engagement feature 240 is about 0.008inches. The height and diameter of the engagement features 240 can beincreased to increase retention force. In some embodiments, increasingthese dimensions may be limited by the force required to advance theconnector 200 into the catheter 100, which is generally done manually.

Another aspect of the engagement feature 240 is the length thereof or ofindividual portions thereof. For example, one embodiment has two barbsas discussed above. In one arrangement a distal-most barb is about 0.065inches in length, though longer barbs could be used. In one embodiment,a proximal-most barb is about 0.065 inches in length. The proximal-mostbarb can be shorter or longer. For example, in one embodiment, theproximal-most barb is about 0.040 inches in length. In one embodiment,the distal-most barb is 0.065 inches and the proximal most barb is 0.040inches.

Two additional features that contribute to the connection in someembodiments are the spacing between the barbs 244, 248 and the distancethat the catheter is advanced past the proximal most barb.

FIG. 5 demonstrates performance of various barb spacings. Oneconfiguration was tested with a maximum peak to peak barb spacing ofabout 0.740 inches. This chart shows a general trend of increase inretention force for greater barb spacing. Some of the increase in forceobserved in the chart could be attributable to a greater length ofcatheter in contact with the connector apparatus. As the barb spacingincreased, so did the total length of connected catheter. FIG. 5 can beinterpreted to indicate a minimum spacing of approximately 0.100 inchesin some embodiments. At lesser barb spacings than this value theretention force drops rapidly. However, at increased spacings greaterthat this value, the force increases more slowly. In FIG. 5, onetechnique computed the rates of change as about 7 lbs/0.040 inchesbefore an inflection point and about 1.2 lbs/0.040 inches after thecritical point. This analysis employed a simple linear fit. One skilledin the art will recognize that a more complex fit of the data wouldproduce a different mathematical description of the data. However, it isexpected that other such curve fits would still reveal a relativelysteep slope toward 0.100 inches and a flatter slope toward the middle ofthe data. Similarly in FIG. 6, discussed below, a more complex curve fitmight reveal a generally asymptotic profile at one or both ends of thedata set.

FIG. 5 shows that the dual barb configuration has superior connectionstrength to a single barb at all barb spacings and more than twice thestrength once the peak to peak spacing exceeds about 0.100 inches. Also,the difference between bare silicone and braid reinforced silicone isapparent in FIG. 5. Note that in addition to the superior performance atany barb spacing, the slope of the line is greater for a braidedcatheter. This may be due in part to an amplified retention forcegenerated by the combination of the retention feature 240 and thebraided structure 140 in the catheter 100 upon connection of thecatheter to the connector 200. This highlights the superiority of thebraided flexible catheter over alternative designs. More particularly,the braided structure has much greater retention strength for a givenbarb dimension compared to a non-braided catheter of identical material.Also, the braided structure has the ability to further increase theretention strength by the use of multiple barbs on the connector 200.Also, the use of the braided structure compared to other reinforcementsfacilitates the use of barbs and optimized barb geometry on theconnector 200. Moreover, the use of a soft elongate body 112 in thecatheter 100 allows the braided structure 140 to neck down behind thebarb and thereby increase the retention strength.

Given the results illustrated in FIG. 5, the spacing can be any suitablespacing, but as discussed below preferably is at least about 0.100inches in an arrangement with two barb, or more. In one embodiment, thespacing between the peaks of adjacent barbs 244, 248 is about 0.229inches. In one embodiment, the spacing between the peaks is about 0.240inches.

Although FIG. 5 illustrates the vast improvements that can be achievedwith the embodiments described above, in some applications an engagementmechanism having less redundancy provides adequate retention force. Forexample, FIG. 5 shows one embodiment where an engagement mechanism witha single barb provides about 10 pounds of retention force. This amountof force is sufficient for some applications. Also, although FIG. 5shows that bare silicone generally provides a much lower retention forcefor various dual barb arrangements a combination of bare silicon and aconnector can be sufficient in some arrangements, such as if thesilicone is clamped at an outside surface thereof.

In various embodiments, it is preferable to advance the catheterproximally past the proximal-most barb. The sensitivity to this variableis illustrated by FIG. 6. Also, a single barb example is illustrated inFIG. 6. The dual barb variable setup demonstrated little or no increasein retention force when the amount past the barb exceeded about 0.125inches for one embodiment. This suggests that a suitable range for thecatheter connection past the barb could be about 2-3 mm (0.080″-0.120″)or about 1.5-4 mm (0.060″-0.160″) for one embodiment of the catheter andconnector combination.

FIG. 6 shows that a catheter flush with the proximal side of the secondbarb exceeds the retention strength of a single barb where the catheteris about 0.125 inch or less beyond the proximal side of the single barb.Other embodiments provide advancement beyond the retention feature 240of between about 0.080 inches and 0.120 inches. In some embodiments, itis preferable to advance the catheter proximally past the proximal-mostbarb by between about 0.060 inches and 0.160 inches. In someembodiments, it is preferable to advance the catheter proximally pastthe proximal-most barb by about 0.010 or about 0.111 inches. In someembodiments, it is preferable to advance the catheter proximally pastthe proximal-most barb by between at least about 0.125 inches.

As discussed above, the engagement mechanism 32 particularly whenconfigured to include portions of the catheter 100 and the connector 200provides a number of clinical advantages over other arteriovenous shuntdevices. Specifically, the combination of at least one of a braidedstructure and a barb in the engagement mechanism improves the ease ofuse of the device. As discussed above, the catheter 100 can be cut andconnected without the need to further modify a catheter prior toconnection. Also, the embodiments discussed herein have improvedconnectability in that a lesser force can be used to connect theengagement mechanism 32 than would be sufficient to disconnect themechanism. Also, the system 10 is “one-size-fits-all” because it isconfigured to be trimmed to any desired length.

Other advantages that are provided include improved durability. Thecatheter 100 has many independent braided members 152 within the braidedstructure 140. The plurality of braided members 152 provides redundantsupport, which results in improved resistance to clamping and fatiguefracture. The plurality of braided members 152 also provides improvementin tensile strength. Compared to other prior approaches, lessmanufacturing steps are required, reducing the labor and cost ofproduction. Also, it is expected that at least some of the embodimentsof the catheter 100 withstand higher radial loads before collapsing andcan be placed in a tighter radius without kinking than was possible withprior devices. In at least some applications, improved burst resistance(the ability to withstand high pressures without detaching from theconnector or rupturing) can be advantageous but is not required.

Other advantages of the embodiments discussed herein include a benefitfor the physician to receive feedback indicating that the catheter hasbeen properly connected. For example, the multiple barb system providesincrease in strength even when the catheter is minimally past a secondbarb. Visible deformation, e.g., by expansion of the catheter 100 or thebraided structure 140, serves as a visual indication of properattachment. This allows the user to observe the visible reference toinsure that the catheter is past both barbs by referencing the twovisible rings as the braided catheter goes over the first and secondbarbs. If not visible, this expansion can create ribbed portion on theotherwise smooth outer surface of the catheter 100 to provide a tactileconfirmation of proper attachment.

Although it is recommended that the catheter be fully advanced againstthe central enlarged segment 250 of the connector 200, the integrity ofthe connection provides sufficient strength if inserted less than thisamount, e.g., by only one-half of the distance from the barb 248 to thesegment 250. This is expected to result in strength that is almostdouble when compared to a similar single barb system. When fullyinserted it is expected that the strength will be almost tripled.

As discussed above, multiple and single barb engagement features can besuitable for secure connections. A properly designed single barb andbraided catheter connection system can be made very secure, e.g., withabout six times the retention force as a catheter made from the samematerial but without the braid. The second barb is expected to add atleast a 100% increase in retention strength. This makes the engagementmechanism more robust, providing the added benefit of reducing theurgency of optimal insertion of the catheter over the connector to theenlarged section 250.

These features provide the desired level of security while providing theend user with both an increase in the confidence of achieving a secureconnection.

1.-31. (canceled)
 32. A method of assembling a blood flow conduitin-situ, comprising: providing a connector system comprising a firstengagement feature located on a connecting structure of a proximal bloodconduit portion and distal blood conduit portion including a cathetercomprising a proximal end portion in which a braided structure isembedded; and cutting the catheter through the braided structure to sizethe catheter in-situ.
 33. The method of claim 32, wherein the proximalblood conduit portion further comprises a connector having a distalsegment including a retention feature, and further comprising advancingthe catheter over the distal segment of the connector until at least aportion of the braided structure is positioned proximal of the retentionfeature.
 34. The method of claim 32, further comprising advancing thecatheter proximally relative to the distal segment of the connectoruntil the retention feature is surrounded by the catheter and a portionof an outer surface of the catheter is raised indicating sufficientadvancement of the catheter relative to the distal segment of theconnector.
 35. The method of claim 33, wherein the braided structureapplies a compressive force on the retention feature when the catheteris advanced sufficiently relative to the distal segment of the connectorto enhance the connection of the catheter with the connector.
 36. Amethod of assembling a blood flow conduit in-situ, comprising: providinga connector system comprising: a first blood conduit having a engagementfeature located adjacent to an end thereof; and a second blood conduitcomprising a tubular body having a braided structure disposed therein,the braided structure having a first configuration in a free state; andmoving the tubular body and engagement feature relative to each othersuch that a portion of the braided structure is in a secondconfiguration different from the first configuration permitting thetubular body to be axially aligned with the engagement feature; andpermitting the braided structure to relax to a configuration differentfrom the first configuration such that the engagement feature and thetubular body are connected by a connection force applied therebetween.37. The method of claim 36, wherein the first blood conduit comprises aconnector body.
 38. The method of claim 37, wherein the first bloodconduit comprises a vascular graft connected to the connector body. 39.The method of claim 36, further comprising cutting the catheter througha proximal portion of the tubular body to size the catheter in-situ. 40.The method of claim 39, wherein the tubular body has a proximal end andthe braided structure is disposed along a length of the tubular bodyadjacent to but spaced from the proximal end.
 41. The method of claim36, wherein the braided structure and engagement feature are configuredsuch that moving the tubular body and engagement feature into engagementrequires less force than moving the tubular body and engagement featureout of engagement.
 42. A catheter for insertion into a blood vessel at avessel insertion site for delivering blood after dialysis to a locationdownstream of the vessel insertion site, the catheter comprising: anelongate body having a proximal portion, a distal portion, and a lumenextending therebetween along a longitudinal axis, the elongate bodybeing flexible and having an inner surface surrounding the lumen and anouter surface surrounding the inner surface; and a braided structurehaving a proximal end and a distal end, the braided structure beingembedded within the elongate body such that the outer surface of theelongate body completely surrounds the braided structure, the braidedstructure extending from the proximal portion of the elongate bodytoward the distal portion thereof and having a first configuration in afree state, wherein a portion of the braided structure is adapted to bein a second configuration different from the first configuration whenthe proximal portion of the elongate body and the braided structure arebrought in to contact with an engagement feature of a second bloodconduit, the portion of the braided structure further adapted to relaxto a configuration different from the first to provide an enhancedconnection between the proximal portion of the elongate body, thebraided structure and the engagement feature, wherein a proximal lengthof the tubular body comprises a sizing region configured to be cut insitu to adapt the overall length of the tubular body; and wherein in atleast one configuration the braided structure is spaced axially from theproximal end of the tubular body.
 43. The catheter of claim 42, whereinthe braided structure is spaced axially from the proximal end of thetubular body prior to being cut to size.
 44. The catheter of claim 42,wherein a proximal length of the tubular body comprises an outercircumferential surface, and an end surface; and wherein at least one ofthe outer circumferential surface and the end surface present a smoothconfiguration.
 45. The catheter of claim 42, wherein the elongate bodyis configured to minimize delamination or other separation thereof fromthe braided structure.